Adaptive Fragmentation for HARQ in Wireless OFDMA Networks

Abstract

A method performs a hybrid automatic repeat-request (HARQ) operation in a wireless orthogonal frequency division multiple access (OFDMA) network. A quality of a channel between a transmitter and a receiver is estimated as an error metric. A packet for the HARQ operation is fragmented adaptively at the transmitter according to the estimated error metric. The fragmentation is performed at the HARQ layer when the error metric is less than a predetermined threshold, otherwise the fragmentation is performed at the MAC layer.

Description

FIELD OF THE INVENTION[0001]This invention relates generally to mobile wireless networks, and in particular to a system and method of adaptive fragmentation for hybrid automatic repeat request (HARQ) operations on wireless channels of OFDMA networks.BACKGROUND OF THE INVENTION[0002]OFDM[0003]Orthogonal frequency-division multiplexing (OFDM) is frequently used to reduce multi-path interference in a physical layer (PHY) of channels of wireless communication networks. OFDM is specified for a number of wireless communications standards, e.g., IEEE 802.11a / g and IEEE 802.16d / 16e.[0004]OFDMA[0005]Based on the OFDM, orthogonal frequency division multiple access (OFDMA) has been developed. With OFDMA, a separate sets of orthogonal tones (frequencies) are allocated to multiple transceivers (users) so that these transceivers can engage in parallel communication. For example, the IEEE 802.16 / 16e standard has adopted OFDMA as the multiple channel access mechanism for non-line-of-sight (NLOS) co...

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Benefits of technology

[0024]The fragmentation operations are dynamically adapted depending on an error metric (EM) of a channel quality between stations. For example, as the quality of a channel decreases, the bit error rate increases (BER), and as the quality increases the BER decreases. The BER also affects the packet error rate (PER). The quality of a channel can also be expressed in terms of the inverse signal-to-noise ratio (ISNR), which is 1 / SNR. A lower ISNR usually means a lower BER, and a higher ISNR a higher BER.

[0025]More specifically, fragmentation is performed at the MAC layer with respect to the length requirement of a HARQ forward error correction coding (FEC) block when the error metric is greater than a predefined threshold (TH). Thus, no fragmentation at the HARQ layer is needed. When the error metric is less than the threshold, fragmentation is performed at the HARQ layer, rather than at the MAC layer.

Problems solved by technology

This setting can lead to considerable resource underutilization on relay link in mobile multihop relay networks wherein higher capacity is provisioned.

Moreover, the resource underutilization in current ARQ protocol will further deteriorate in the next generation advanced IEEE 802.16 network (e.g., IEEE 802.16m), wherein an even higher transmission rate will be used.

However, this static fragmentation can result in a degradation of the system performance over channels with time-varying quality incurred by mobility or channel fading.

This is a serious problem for the relay link of a multihop relay network, and for next generation advanced IEEE 802.16 networks (e.g., IEEE 802.16m), as high capacity is one of the requirements for such networks.

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